1. Field of the Invention
The present invention relates to a webbing retractor for use in the vehicle and including an emergency locking retractor (hereafter abbreviated as ELR) and an automatic locking retractor (hereafter abbreviated as ALR).
2. Description of the Related Art
There are webbing retractors including those with ELR function and ALR function. The ELR function enables the drawing out and retracting of an occupant securing webbing in a normal condition, and blocks the drawing-out of the webbing when a vehicle rapidly decelerates. The ALR function blocks the drawing-out of the webbing at any time after mounting the webbing irrespective of the conditions.
In the webbing retractors constructed as set forth above, there are well-known conventional webbing retractors as will now be described. A winding shaft is rotatably supported by a frame. It is possible to retract the occupant securing webbing around the winding shaft. A lock ring is provided for the winding shaft through a spring member. The lock ring is rotatable according to the movement of the winding shaft by the urging force of the spring member, and is relatively rotatable with respect to the winding shaft by resisting the loaded force of the spring member.
A lock plate is provided for the lock ring so as to be rotatable with the lock ring. A ratchet wheel secured to the frame, is disposed around the lock plate. Further, the webbing retractor is provided with acceleration detecting means which prevents the rotation of the lock ring when the vehicle rapidly decelerates. The rotation of the lock ring is blocked so that relative rotation is caused between the winding shaft and the lock ring against the urging force of the spring member. Accordingly, external teeth of the lock plate engage internal teeth of the ratchet wheel.
As set forth above, in a normal condition, the occupant can easily drive since the webbing can be freely retracted and drawn-out from the winding shaft. Further, when the vehicle rapidly decelerates, the drawing-out of the webbing is blocked so that the occupant is secured.
On the other hand, an ALR lever is provided so as to employ a lock mechanism of the winding shaft as ALR. The ALR lever is provided with a switching pawl including an engaging claw for removably engaging external teeth provided on an outer periphery of the lock ring, and a releasing arm provided for the switching pawl on an end opposed to the engaging claw. When the releasing arm is pressed, the ALR lever is rotated about a supporting pin provided at a boundary portion between the switching pawl and the releasing arm. Consequently, a condition where the engaging claw is removed from the external teeth of the lock ring, i.e., an ELR condition is changed into a condition where the engaging claw engages the external teeth of the lock ring, i.e., an ALR condition. Further, in the webbing retractor, a cam is used as means for pressing the releasing arm. The cam is driven by the rotation of a decelerating gear for decelerating the rotation of the winding shaft.
A substantially maximum amount of the webbing must be drawn-out in order to switch over the lock mechanism of the winding shaft from ELR to ALR. When a substantially maximum amount of the webbing is drawn-out, the rotation of the winding shaft in the webbing drawing-out direction is transmitted according to the movement of the webbing to the cam via the decelerating gear. Hence, the releasing arm is pressed by the cam so that the ALR lever is rotated about the supporting pin so as to engage the engaging claw engaging the external teeth of the lock ring with the external teeth. As a result, the lock mechanism is switched over to ALR.
However, as set forth above, in the conventional webbing retractor, the lock mechanism is switched over from ELR to ALR by the pressing of the releasing arm by the cam when a substantially maximum amount of the webbing is drawn-out. Therefore, it is necessary to provide high dimensional accuracy of the cam so as to reliably press the releasing arm, and high dimensional accuracy of the decelerating gear so as to enable the transmission of the force for pressing the releasing arm to the cam when a substantially maximum amount of the webbing is drawn-out. Further, the cam and the decelerating gear has to be assembled with a high assembling accuracy. Thus, it has been complicated to manufacture and assemble the cam and the decelerating gear.
As described hereinbefore, the lock mechanism must be reliably switched over from ELR to ALR. That is, it is necessary to provide a slightly elongated webbing so as to avoid a condition where the lock mechanism can not be switched over from ELR to ALR even though the maximum amount of the webbing has been drawn-out. As a result, there are drawbacks due to increased cost and the like.